In the processing of oleaginous seeds to extract oil by solvent extraction, the seeds are crushed, milled or otherwise fragmented (i.e., made into cakes, flakes etc.) and are treated with a solvent to extract the oil, leaving a solvent extracted material (i.e., a particulate material, e.g., a meal) in which vaporizable solvent remains. By heating the meal using steam both indirectly as by a heated surface and/or directly by intimate steam contact with the meal, the solvent is removed therefrom by vaporization while the "wet" meal is dried and otherwise processed to deactivate certain types of enzymes and to denature proteins to thereby produce an edible substance.
The prior art generally discloses processes and apparatus wherein the material from which the solvent is to be removed progresses downwardly as a bed through a column which is provided with spaced horizontal plates therein dividing the interior of the column into a vertical series of compartments. In these compartments, the material is heated and agitated, with the finished material discharged from the bottom of the column and the solvent being removed as an overhead vapor from the column for subsequent condensing, with or without pre-conditioning or treatment.
Present desolventizing practice includes counter-current processing using a direct contacting flow of steam. Steam is distributed within the column such that it condenses on the particulate material while vaporizing some quantity of solvent adhered thereupon, further providing sensible heat to raise the temperature of the particulate material.
Generally, the moisture content of the particulate material exiting the desolventizer is from about 15 to 25 weight percent and is a function of prior solvent content, other moisture content, the ratio of direct steam to indirect steam used in the process, and the exit temperature. Drying is generally required to produce commercially saleable meal, with moisture reduction on the order of 25 to 33 percent being necessary so as to produce a commercial product having a moisture content of about 10-12 weight percent.
A shortcoming of known desolventizing practice is a small but significant quantity of the moisture content needing to be removed from the meal exiting the desolventizer is solvent. Customarily, a portion of the residual solvent remaining with the meal after desolventizing is driven off (i.e., vaporized) in subsequent drying steps, along with the condensed steam adhered or carried by the meal exiting the desolventizer.
Heretofore, no known desolventizing process or single apparatus has satisfactorily minimized atmospheric solvent vapor discharge, reduced the quantities of make-up to the recycle solvent stream and reduced the capital and operating costs of desolventizing operations as contemplated by the apparatus and process of this invention.